Air-driven engines such as aircraft engines typically include components that alter, direct, and/or guide the flow of air to improve performance. These components are generally positioned using an actuator. The actuator can be a conventional hydraulic actuator or a more specialized “fueldraulic” actuator which uses fuel as a hydraulic fluid. In either case, the actuator is called upon to move the air-directing components into one of a variety of positions such that the flow of air is directed through the engine as needed.
In order to ensure that the air-directing components have been appropriately positioned, the actuator typically includes a position sensor and a controller (e.g., an integrating controller, a proportional controller, and the like). The position sensor senses an actual position of the actuator, which directly correlates to the actual position of the air-directing component, and the controller ensures that a commanded position for the actuator matches the actual sensed position. Since the actual position of the air-directing component is determined based on information provided by the position sensor, the accuracy of the position sensor is important.
In many applications, the actuators are equipped with a position sensor known as a linear variable differential transducer (LVDT). The LVDT is an electronic device that outputs a particular electrical position feedback (e.g., an induced voltage) depending on position. By observing the electrical position feedback for one or more characteristics (e.g., magnitude and phase change), the position of the actuator and, more importantly, the position of the air-directing component can be determined. Therefore, as the actuator continually moves and transitions the air-directing component into one of a variety of possible positions, the LVDT operably coupled to the actuator generates a varying electrical position feedback that can be correlated to a varying position of the air-directing component.
Unfortunately, the LVDT's employed by the actuators are costly, both in terms of time and money, and are relatively heavy. The LVDT's are also relatively large in physical size and require a vast amount of space to be added to the actuator. In many circumstances, the LVDT's are so generously proportioned that the actuators have to be made much larger than functionally required to accommodate and house the LVDT's. Also, the LVDT's use small gauge wires that are prone to failure. Therefore, when using the LVDT as the position sensor, additional redundancy (e.g., two separate position sensors) is usually built into the positioning system. This added redundancy increase the overall cost of meeting strict reliability requirements. In an aircraft environment, the excessive size and weight and failure modes are detrimental to the life cost of the aircraft. In addition, the LVDT's generally require complex circuitry to provide the proper input signal as well as to demodulate the output signal. From the foregoing, it can be appreciated that the actuators using the LVDT's to sense the position of the air-directing components have significant drawbacks.
From the foregoing, it can be seen that an actuator that employs a relatively small, lightweight sensor adapted to sense the position of an air-directing component in a cost-efficient and reliable manner would be desirable. The invention provides such an actuator. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.